Circuit Description
in order to provide the best possible combination of driveability, fuel economy, and emissions control, a closed loop air-to-fuel metering system is used. While in closed loop, the powertrain control module (PCM) monitors the HO2S 1 signal and adjusts the fuel delivery based upon the HO2S signal voltage. A change made to fuel delivery will be indicated by the long-term and the short-term fuel trim (FT) values, which you can monitor with a scan tool. The ideal fuel trim values are approximately 0 percent. If the HO2S signals indicate a lean condition the PCM will add fuel, resulting in fuel trim values that are more than 0 percent. If a rich condition is detected, the fuel trim values will be less than 0 percent, indicating that the PCM is reducing the amount of fuel delivered. If an excessively rich condition is detected, DTC P0172 will set.
The maximum authority of the PCM to control the long-term FT allows a range between -23 percent and +16 percent. The maximum authority of the PCM to control short-term FT allows a range between -11 percent and +20 percent. The PCM monitors fuel trim during various operating conditions before determining the status of the fuel trim diagnostic. The fuel trim cells are used to determine fuel trim are as follows:
VIN K
| • | Idle, purge commanded |
| • | Deceleration, purge commanded |
| • | Normal driving, purge commanded |
| • | Normal driving, no purge commanded |
| • | Idle, no purge commanded |
VIN 1
| • | Idle, purge commanded |
| • | Normal driving, purge commanded |
| • | High flow driving, purge commanded |
| • | Normal driving, no purge commanded |
| • | Idle, no purge commanded |
You may need to operate the vehicle during all of the above conditions before the PCM determines the fuel trim status. The amount that fuel trim deviates from 0 percent in each cell, and the amount that each cell is weighted directly affect whether or not the vehicle must be operated in all of the cells described above in order to complete the diagnostic.
Conditions for Running the DTC
| • | The following DTCs are NOT set: |
| - | Vehicle speed sensor (VSS) |
| - | Throttle position (TP) sensor |
| - | Evaporative emission (EVAP) system |
| - | Heated oxygen (HO2) sensor |
| - | Engine misfire |
| - | Intake air temperature (IAT) sensor |
| - | Manifold absolute pressure (MAP) sensor |
| - | Idle speed |
| - | Fuel injectors |
| - | Ignition control (IC)/Bypass |
| - | Exhaust gas recirculation (EGR) pintle position |
| - | EGR flow |
| - | Engine coolant temperature (ECT) sensor |
| - | Crankshaft position (CKP) sensor |
| - | Camshaft position (CMP) sensor |
| - | Mass air flow (MAF) sensor |
| • | The engine coolant temperature is between 20°C (68°F) and 110°C (230°F). |
| • | The intake air temperature is between -18°C (0°F) and 70°C (158°F). |
| • | The BARO is more than 70 kPa. |
| • | The manifold absolute pressure is between 15 kPa and 85 kPa. |
| • | The throttle angle is less than 90 percent. |
| • | The vehicle speed is less than 82 mph. |
| • | The mass air flow is between 3 g/s and 150 g/s. |
| • | The engine speed between 600 RPM and 4000 RPM. |
Conditions for Setting the DTC
| • | The long-term FT is at or near the maximum authority of -23 percent. |
| • | The short-term FT is at or near the maximum authority of -11 percent. |
| • | VIN K --All conditions have been met in Fuel Trim Cells 1, 2, 6, 9 and/or 10. |
| • | VIN 1--All conditions have been met in Fuel Trim Cells 2, 4, 6, 9 and/or 10. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect the following items:
| • | The EVAP canister--Inspect the EVAP canister for fuel saturation. If the canister is full of fuel, inspect the EVAP and the fuel system components for damage. Refer to Idle Air Control (IAC) System Diagnosis . |
| • | The mass air flow sensor--Disconnect the MAF sensor and see if the rich condition is corrected. If so, replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . |
| • | The fuel pressure regulator--Inspect for a leaking fuel pressure regulator diaphragm by inspecting the vacuum line to regulator for the presence of fuel. If you find a problem, replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement . |
| • | The TP sensor--An intermittent TP sensor output will cause the system to go rich due to a false indication of the engine accelerating. The throttle angle that is displayed on a scan tool should increase steadily from 0 percent to 100 percent when you open the throttle. If not, inspect the TP sensor for loose mounting screws. If the TP mounting screws are OK, replace the TP sensor. Refer to Throttle Position Sensor Replacement . |
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
DTCs other than DTC P0172 may indicate the presence of a condition which may cause a rich condition. If this is the case, repairing the condition which caused the other DTC will most likely correct the DTC P0172.
-
If the DTC P0172 test passes while the Fail Records conditions are being duplicated, the rich condition is intermittent. Refer to Diagnostic Aids for additional information on diagnosing intermittent conditions.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | ||
Are any other DTCs set? | -- | Go to applicable DTCs | ||
3 |
Are the values more negative than the specified value? | -10% | ||
Does the DTC reset? | -- | Go to Diagnostic Aids | ||
5 | Inspect the air filter element and replace as necessary. Refer to Air Cleaner Element Replacement . Did you find and correct the condition? | -- | ||
6 | Inspect the air intake duct for being collapsed or restricted. Repair the condition as necessary. Refer to Air Cleaner Inlet Duct Replacement . Did you find and correct the condition? | -- | ||
7 |
Did you find and correct the condition? | -- | ||
8 | Start the engine, and note the idle quality. Is the idle low or unsteady? | -- | ||
9 | With the engine idling, observe the Idle Air Control with a scan tool. Does the value measure less than the specified value? The value is displayed in counts. | 100 | ||
10 |
Did you find and correct the condition? | -- | ||
11 |
Did you find and correct the condition? | -- | ||
12 |
Did you complete the replacement? | -- | ||
13 |
Does the TP Angle increase steadily and evenly from the minimum value at closed throttle to the maximum value at wide-open throttle? | 0%-100% | ||
14 |
Are both values near the specified value? | 0% | ||
15 |
Did you find and correct the condition? | -- | ||
16 |
Did you find and correct the condition? | -- | ||
17 |
Did you find and correct the condition? | -- | ||
18 |
Did you complete the replacement? | -- | Go to Diagnostic Aids | |
19 |
Did you complete the repair/replacement? | -- | -- | |
20 | Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the replacement? | -- | -- | |
21 |
Does the DTC reset? | -- | System OK |
